1. Field of the Invention
This invention relates to the recovery of oil from oil shale and more particularly to a distillation process for oil recovery involving treatment of ground oil shale with a hot gas in a cyclone reactor followed by separation of the oil.
2. Description of the Prior Art
Numerous methods are known for distillation (retorting) of oil shale. In these the oil shale is heated, thereby breaking down the kerogen contained in the shale so that it can be extracted in the form of gaseous and liquid hydrocarbons. Depending on the hydrogen content of the oil shale, a larger or smaller amount of the organic substance can be extracted. A certain amount always remains in the shale as residual carbon. In the interest of the most complete utilization of the energy content of the oil shale, this carbon should also be used as an energy source.
Many methods use the shaft furnace principle for distillation, for example, as described in U.S. Pat. No. 3,736,247, and German-AS No. 22 43 389. The disadvantage of this method is that fine material necessarily accumulating during size reduction cannot be utilized. In addition, complete burning off of the residual carbon is made very difficult due to the requisite size of charge materials. What is more, the oil vapor and the distillation gas are exposed for an extended time to the distillation temperature, thus causing cracking reactions which reduce the yield and the quality of oil.
The shaft furnace principle cannot be used with more finely crushed material. Other methods using fine material, e.g., U.S. Pat. No. 3,844,930, operate with solid materials as heat conductors. The circulating quantity of heat conductor, which includes an amount several times as large as the amount of shale, further increases the amount of solid material that must be handled.
The German OS's Nos. 27 28 204 and 27 28 455 teach a process of pyrolysis of carbon-containing material, including oil shale, in a cyclone-reactor using solid material heat conductors as described above. Carbon-containing material with a granular size of less than 1 mm is introduced into a cyclone reactor in a carrier gas stream at speeds of 20-76 m/sec. Before or upon entry into the cyclone, this gas stream is combined with a second gas stream containing hot solid particles which serve to heat the carbon-containing material to distillation temperature. The weight relationship of the solid material used for heating to the carbon-containing material should be between 2 and 20. After a short contact time (calculated as the average time that the carrier gas is in the cyclone) of less than ca. one second, particularly between 0.1 and 0.6 sec., the distillation gas, mixed with the carrier gas, is removed from the solid materials, i.e., heat conductor particles and distillation residue.
With this known method the distillation gases are mixed and diluted with the carrier gases, making their processing more difficult. The distillation residue leaves the cyclone mixed with the solid material heat conductors, so that when it is further processed large amounts of ballast must be carried along with it.
Thus, an oil shale recovery method using distillation is needed that allows recovery of the gas and solid portions without requiring their dilution and thereby further separation.